This invention relates to removable pressure sensitive adhesives based on aqueous emulsions. The removable pressure sensitive adhesives of the invention have enhanced resistance to water-whitening.
Removable pressure sensitive adhesives are used on a variety of products including labels, tapes, films, and the like, to enable the product to adhere to a substrate and then to later be removed from the substrate without difficulty and without leaving a stain or residue. To be suitable for such applications, the pressure sensitive adhesive must have good adhesion with low peel strength and must not exhibit a significant increase in adhesion over time. Optimally, the pressure sensitive adhesive should exhibit such physical properties on a variety of substrates. Typical commercially available aqueous acrylic emulsion pressure sensitive adhesives that are removable cannot be used with film facestocks which are used in outdoor applications. One outdoor application involves decorative decals which are applied to substrates such as glass. One technique for applying such a decorative decal to a substrate is to spray water on the adhesive and/or substrate so that the decal is slidingly movable over the substrate for ease of positioning. Unfortunately, in such a technique, the aqueous acrylic emulsion adhesive film turns milky in contact with water. Another outdoor application involves protective films that are applied via adhesive to materials for construction projects where the film serves to protect the construction material until the construction project is completed. Exposure of the protective film covered construction materials to water or high humidity in outdoor environments often results in the aqueous acrylic emulsion adhesive turning milky. For transparent filmstocks, this water-whitening results in an unsatisfactory appearance.
For a successful aqueous acrylic emulsion removable pressure sensitive adhesive to be used with decorative or protective films and decals in outdoor applications, the adhesive needs to exhibit good water resistance along with good anchorage of the adhesive to the film facestock to assure clean removability from the substrate. The current commercially available aqueous acrylic emulsion pressure sensitive adhesives which demonstrate good water-whitening resistance are permanent adhesives, i.e. those that leave an adhesive residue on the substrate if the facestock is removed. Currently available removable aqueous acrylic emulsion pressure sensitive adhesives which demonstrate good anchorage to the film also exhibit poor water-whitening resistance. Accordingly, there is a need for an aqueous acrylic emulsion pressure sensitive adhesive which exhibits both desired properties of removability and water-whitening resistance.